There are numerous forms of prior art lock pins adapted to retain an insert having a central aperture on a holder including a shoulder and replaceable shim seat for the bottom of the insert. In one common version, a conical taper screw head engages the curved opening of an "ISO" aperture in the insert providing a straight axial threaded retention screw normal to the bottom seat. Under certain conditions, the screw may unwind due to the cutting force direction; on other occasions the forces tend to rotate the insert and tighten the screw to the extent that it shears off.
In another design, a similar uniformly headed unthreaded lock pin having a sliding fit in an unthreaded bore in the holder is notched for engagement by an angular set screw forcing the pin down. In this case the lock pin must be completely removed to replace the insert with no means for preventing the pin and shim from falling out when the set screw is backed off.
In a third case, a holddown screw with uniform tapered head is threaded into the holder at a angle with the thread and head size small enough to permit insert removal upon loosening. Each screw has strength limitations in providing a small enough size to accommodate loose pin insert removal. It is again possible in the case of a round insert for cutting forces on the insert to unwind or overtighten the screw.
In another design, a right angle "skiboot" pin configuration is provided with an offset insert engaging projection accommodating insert removal upon loosening with a fulcrum in the holder for the heel of the pin and a threaded screw adapted to apply leverage pressure on the "toe" of the pin. A shim retention bushing is provided which may get lost when the insert is removed. This is an expensive design but is otherwise satisfactory in providing desirable retention features.
Another variation feature an angularly bent pin with uniform conical head having fulcrum shoulder at the bend and screw engagement at the end to tilt the pin head into retaining engagement with the insert. This construction requires pin removal to replace the insert and has no shim retaining feature.
There are three pin retention designs commercially sold under the trademark "Tizit Maxilock K, P and S". They all involve uniform threaded straight retention pins with shaped heads and fulcrum shoulders either engaging special bushings or involving extra holddown clamps. These constructions are relatively expensive and may loosen or overtighten under cutting forces when applied to round inserts.
On the whole this is a crowded art with many additional variations such as disclosed in the following prior art reference patents; U.S. Pat. Nos. 3,314,126 (Stier); 3,316,616 (Milewski); 3,341,921 (Weller et al); 3,355,786 (Hargreaves); 3,490,117 (Hertel); 3,662,444 (Erkfritz); 3,848,303 (Faber); 3,908,255 (Faber); 4,044,440 (Stier) and 4,430,031 (Hellstrom).